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Papers by Abdul Haseeb Syed

Research paper thumbnail of A model for low-frequency, anisotropic wind fluctuations and coherences in the marine atmosphere

To assess dynamic loads, large offshore wind turbines need detailed and reliable statistical info... more To assess dynamic loads, large offshore wind turbines need detailed and reliable statistical information on the inflow turbulence. We present a model that includes low frequencies down to sim1\sim 1sim1 hr$^{-1}$ using the observed S(f)proptof−5/3S(f) \propto f^{-5/3}S(f)proptof−5/3 in that range. The presented model contains a parameter representing the anisotropy of the two-dimensional, incompressible turbulence and it assumes the low-frequency fluctuations to be homogeneous in the vertical direction. Combined with a three-dimensional model for the smaller scales, the model can predict correlations between different points. We have validated the model against two offshore wind data sets: a nacelle-mounted, forward-looking Doppler lidar with four beams at the Hywind Scotland offshore wind farm, and sonic anemometer measurements at the FINO1 research platform in the North Sea. One-point auto spectra and two-point cross spectra were calculated after splitting the data into different atmospheric stability classes. The...

Research paper thumbnail of Simulating low-frequency wind fluctuations

Large-scale flow structures are vital in influencing the dynamic response of floating wind turbin... more Large-scale flow structures are vital in influencing the dynamic response of floating wind turbines and wake meandering behind large offshore wind turbines. It is imperative that we develop an inflow wind turbulence model capable of replicating the large-scale and low-frequency wind fluctuations occurring in the marine atmosphere since the current turbulence models do not account well for this phenomenon. Here, we present a method to simulate low-frequency wind fluctuations. This method employs the two-dimensional spectral tensor for low-frequency, anisotropic wind fluctuations presented by Syed and Mann (2023) to generate stochastic wind fields. The simulation method generates large-scale 2D wind fields for the longitudinal u and lateral v wind components. The low-frequency wind turbulence is assumed to be independent of the high-frequency turbulence thus a broad spectral representation can be obtained just by superposing the two turbulent wind fields. The method is tested by comparing the simulated and theoretical spectra and co-coherences of the combined low-and high-frequency fluctuations. Furthermore, the low-frequency wind fluctuations can also be subjected to anisotropy. The resulting wind fields from this method can be used to analyze the impact of low-frequency wind fluctuations on wind turbine loads and dynamic response and for studying the wake meandering behind large offshore wind farms.

Research paper thumbnail of Turbulence above offshore wind farms measured by aircraft

Journal of Physics: Conference Series

The flow inside and around large offshore wind farms may range from smaller and shorter structure... more The flow inside and around large offshore wind farms may range from smaller and shorter structures present due to the mechanical turbulence generated by wind turbines to larger, and longer structures indicative of the mesoscale flow. In this study, we explore the variation in turbulence structures above large offshore wind farms located in the North Sea using the data obtained from a research aircraft. The aircraft was flown upstream, downstream, and above the wind farm clusters. We evaluate the normalized autocorrelation of the wind velocity component in the mean wind direction for transverse separations and the rate of energy dissipation in the inertial subrange for neutral and stable stratification. During the neutral stratification, there is high ambient turbulence in the atmosphere and large values of the energy dissipation rate. The intensity of small-scale turbulence structures is increased above and downstream of the wind farm and it dominates the mesoscale flow structures. ...

Research paper thumbnail of Wind speed and power forecasting of a utility-scale wind farm with inter-farm wake interference and seasonal variation

Sustainable Energy Technologies and Assessments, 2020

Forecasting skills for a wind farm would significantly degrade if the complex wake effects of the... more Forecasting skills for a wind farm would significantly degrade if the complex wake effects of the upstream wind farms are excluded, especially when they are spatially close to each other. In this study, the Weather Research and Forecasting (WRF) model has been used to predict wind speed and power for a wind farm in Pakistan in the presence of wake interference from neighboring wind farms for two different seasons. Forecasting is done for two different cases i.e. without and with inter-farm wake effects, and different statistical error parameters were evaluated based on the real observations. A significant reduction in errors was observed in the latter case. For instance, the mean absolute errors in wind speed prediction were reduced by 7.7% and 14% in June (summer) and January (winter) respectively, by the inclusion of inter-farm wake effects. Similarly, an improved forecast of power output was obtained by incorporating the interaction of upstream wind farms i.e. a reduction of 15% ...

Research paper thumbnail of Optimization of a wind farm by coupled actuator disk and mesoscale models to mitigate neighboring wind farm wake interference from repowering perspective

Applied Energy, 2021

Abstract This study explores the effects of inter-farm wakes and proposes staggering schemes that... more Abstract This study explores the effects of inter-farm wakes and proposes staggering schemes that are most suitable for optimization of existing wind farm arrays to mitigate the effects of compound wakes. The case study considers a total of 9 out of 33 most deteriorated wind turbine for a microscale numerical analysis using the steady-state actuator disk model coupled with the mesoscale boundary condition data. Furthermore, the convective atmospheric boundary layer has also been considered. For vertically staggered layouts, the effect of the inter-farm wakes appeared mild at 100 m, modest at 80 m, and high at 60 m; as the maximum velocity deficit observed under the influence of compound wakes is approximately 13.3%, 14.1%, and 15.2%, respectively. Onsite recorded power data has been used to validate the baseline predicted powers at 80 m hub height. Both vertical and horizontal staggering options have been assessed for partial repowering. By elevating the turbines to a 100 m hub height, the cumulative power generation from the 9 × turbines increased by approximately 13.5% while reducing the hub height to 60 m decreased the power output by approximately 11.5% of that of the baseline at 80 m hub height. Further increase in cumulative power of up to 23% compared to existing layout is achieved by applying a lateral repositioning of 3 × underperforming turbines now positioned at 100 m hub height. This paper hence presents an applied insight for partial repowering of onshore wind farms affected by inter-farm wakes.

Research paper thumbnail of Partial repowering analysis of a wind farm by turbine hub height variation to mitigate neighboring wind farm wake interference using mesoscale simulations

Applied Energy, 2020

Inter-farm wake losses intensify due to uncoordinated wind farm development. • Repowering augment... more Inter-farm wake losses intensify due to uncoordinated wind farm development. • Repowering augments the power generation capacity of existing wind farms. • Mesoscale simulation provides a fast repowering analysis of wind farms. • Power output is increased by varying the hub height of wake affected turbines.

Research paper thumbnail of Turbulence structures and entrainment length scales in large offshore wind farms

. The flow inside and around large offshore wind farms can range from smaller structures associat... more . The flow inside and around large offshore wind farms can range from smaller structures associated with the mechanical turbulence generated by wind turbines to larger structures indicative of the mesoscale flow. In this study, we explore the variation in turbulence structures and dominant scales of vertical entrainment above large offshore wind farms located in the North Sea, using data obtained from a research aircraft. The aircraft was flown upstream, downstream, and above wind farm clusters. Under neutrally stratified conditions, there is high ambient turbulence in the atmosphere and an elevated energy dissipation rate compared to stable conditions. The intensity of small-scale turbulence structures is increased above and downstream of the wind farm, and it prevails the mesoscale fluctuations. But in stable stratification, mesoscale flow structures are not only dominant upstream of the wind farm but also downstream. We observed that the vertical flux of horizontal momentum is the main source of energy recovery in large offshore wind farms, and it strongly depends on the magnitude of the length scales of the vertical wind velocity component. The dominant length scales of entrainment range from 20 to ~60 m above the wind farm in all stratification strengths, and in the wake flow these scales range from 10 m to ~100 m only under near-neutral stratification. For strongly stable conditions, negligible vertical entrainment of momentum was observed even just 2 km downstream of large wind farms. We also observed that there is a significant lateral momentum flux above the offshore wind farms, especially under strongly stable conditions, which suggests that these wind farms do not satisfy the conditions of an "infinite wind farm".

Research paper thumbnail of A model for low-frequency, anisotropic wind fluctuations and coherences in the marine atmosphere

To assess dynamic loads, large offshore wind turbines need detailed and reliable statistical info... more To assess dynamic loads, large offshore wind turbines need detailed and reliable statistical information on the inflow turbulence. We present a model that includes low frequencies down to sim1\sim 1sim1 hr$^{-1}$ using the observed S(f)proptof−5/3S(f) \propto f^{-5/3}S(f)proptof−5/3 in that range. The presented model contains a parameter representing the anisotropy of the two-dimensional, incompressible turbulence and it assumes the low-frequency fluctuations to be homogeneous in the vertical direction. Combined with a three-dimensional model for the smaller scales, the model can predict correlations between different points. We have validated the model against two offshore wind data sets: a nacelle-mounted, forward-looking Doppler lidar with four beams at the Hywind Scotland offshore wind farm, and sonic anemometer measurements at the FINO1 research platform in the North Sea. One-point auto spectra and two-point cross spectra were calculated after splitting the data into different atmospheric stability classes. The...

Research paper thumbnail of Simulating low-frequency wind fluctuations

Large-scale flow structures are vital in influencing the dynamic response of floating wind turbin... more Large-scale flow structures are vital in influencing the dynamic response of floating wind turbines and wake meandering behind large offshore wind turbines. It is imperative that we develop an inflow wind turbulence model capable of replicating the large-scale and low-frequency wind fluctuations occurring in the marine atmosphere since the current turbulence models do not account well for this phenomenon. Here, we present a method to simulate low-frequency wind fluctuations. This method employs the two-dimensional spectral tensor for low-frequency, anisotropic wind fluctuations presented by Syed and Mann (2023) to generate stochastic wind fields. The simulation method generates large-scale 2D wind fields for the longitudinal u and lateral v wind components. The low-frequency wind turbulence is assumed to be independent of the high-frequency turbulence thus a broad spectral representation can be obtained just by superposing the two turbulent wind fields. The method is tested by comparing the simulated and theoretical spectra and co-coherences of the combined low-and high-frequency fluctuations. Furthermore, the low-frequency wind fluctuations can also be subjected to anisotropy. The resulting wind fields from this method can be used to analyze the impact of low-frequency wind fluctuations on wind turbine loads and dynamic response and for studying the wake meandering behind large offshore wind farms.

Research paper thumbnail of Turbulence above offshore wind farms measured by aircraft

Journal of Physics: Conference Series

The flow inside and around large offshore wind farms may range from smaller and shorter structure... more The flow inside and around large offshore wind farms may range from smaller and shorter structures present due to the mechanical turbulence generated by wind turbines to larger, and longer structures indicative of the mesoscale flow. In this study, we explore the variation in turbulence structures above large offshore wind farms located in the North Sea using the data obtained from a research aircraft. The aircraft was flown upstream, downstream, and above the wind farm clusters. We evaluate the normalized autocorrelation of the wind velocity component in the mean wind direction for transverse separations and the rate of energy dissipation in the inertial subrange for neutral and stable stratification. During the neutral stratification, there is high ambient turbulence in the atmosphere and large values of the energy dissipation rate. The intensity of small-scale turbulence structures is increased above and downstream of the wind farm and it dominates the mesoscale flow structures. ...

Research paper thumbnail of Wind speed and power forecasting of a utility-scale wind farm with inter-farm wake interference and seasonal variation

Sustainable Energy Technologies and Assessments, 2020

Forecasting skills for a wind farm would significantly degrade if the complex wake effects of the... more Forecasting skills for a wind farm would significantly degrade if the complex wake effects of the upstream wind farms are excluded, especially when they are spatially close to each other. In this study, the Weather Research and Forecasting (WRF) model has been used to predict wind speed and power for a wind farm in Pakistan in the presence of wake interference from neighboring wind farms for two different seasons. Forecasting is done for two different cases i.e. without and with inter-farm wake effects, and different statistical error parameters were evaluated based on the real observations. A significant reduction in errors was observed in the latter case. For instance, the mean absolute errors in wind speed prediction were reduced by 7.7% and 14% in June (summer) and January (winter) respectively, by the inclusion of inter-farm wake effects. Similarly, an improved forecast of power output was obtained by incorporating the interaction of upstream wind farms i.e. a reduction of 15% ...

Research paper thumbnail of Optimization of a wind farm by coupled actuator disk and mesoscale models to mitigate neighboring wind farm wake interference from repowering perspective

Applied Energy, 2021

Abstract This study explores the effects of inter-farm wakes and proposes staggering schemes that... more Abstract This study explores the effects of inter-farm wakes and proposes staggering schemes that are most suitable for optimization of existing wind farm arrays to mitigate the effects of compound wakes. The case study considers a total of 9 out of 33 most deteriorated wind turbine for a microscale numerical analysis using the steady-state actuator disk model coupled with the mesoscale boundary condition data. Furthermore, the convective atmospheric boundary layer has also been considered. For vertically staggered layouts, the effect of the inter-farm wakes appeared mild at 100 m, modest at 80 m, and high at 60 m; as the maximum velocity deficit observed under the influence of compound wakes is approximately 13.3%, 14.1%, and 15.2%, respectively. Onsite recorded power data has been used to validate the baseline predicted powers at 80 m hub height. Both vertical and horizontal staggering options have been assessed for partial repowering. By elevating the turbines to a 100 m hub height, the cumulative power generation from the 9 × turbines increased by approximately 13.5% while reducing the hub height to 60 m decreased the power output by approximately 11.5% of that of the baseline at 80 m hub height. Further increase in cumulative power of up to 23% compared to existing layout is achieved by applying a lateral repositioning of 3 × underperforming turbines now positioned at 100 m hub height. This paper hence presents an applied insight for partial repowering of onshore wind farms affected by inter-farm wakes.

Research paper thumbnail of Partial repowering analysis of a wind farm by turbine hub height variation to mitigate neighboring wind farm wake interference using mesoscale simulations

Applied Energy, 2020

Inter-farm wake losses intensify due to uncoordinated wind farm development. • Repowering augment... more Inter-farm wake losses intensify due to uncoordinated wind farm development. • Repowering augments the power generation capacity of existing wind farms. • Mesoscale simulation provides a fast repowering analysis of wind farms. • Power output is increased by varying the hub height of wake affected turbines.

Research paper thumbnail of Turbulence structures and entrainment length scales in large offshore wind farms

. The flow inside and around large offshore wind farms can range from smaller structures associat... more . The flow inside and around large offshore wind farms can range from smaller structures associated with the mechanical turbulence generated by wind turbines to larger structures indicative of the mesoscale flow. In this study, we explore the variation in turbulence structures and dominant scales of vertical entrainment above large offshore wind farms located in the North Sea, using data obtained from a research aircraft. The aircraft was flown upstream, downstream, and above wind farm clusters. Under neutrally stratified conditions, there is high ambient turbulence in the atmosphere and an elevated energy dissipation rate compared to stable conditions. The intensity of small-scale turbulence structures is increased above and downstream of the wind farm, and it prevails the mesoscale fluctuations. But in stable stratification, mesoscale flow structures are not only dominant upstream of the wind farm but also downstream. We observed that the vertical flux of horizontal momentum is the main source of energy recovery in large offshore wind farms, and it strongly depends on the magnitude of the length scales of the vertical wind velocity component. The dominant length scales of entrainment range from 20 to ~60 m above the wind farm in all stratification strengths, and in the wake flow these scales range from 10 m to ~100 m only under near-neutral stratification. For strongly stable conditions, negligible vertical entrainment of momentum was observed even just 2 km downstream of large wind farms. We also observed that there is a significant lateral momentum flux above the offshore wind farms, especially under strongly stable conditions, which suggests that these wind farms do not satisfy the conditions of an "infinite wind farm".